Recent advances in the field of combustion science have demonstrated that organic liquids can be smoldered. When smoldering combustion is applied for the remediation of contaminated soils it is known commercially as the Self-sustaining Treatment for Active Remediation (STAR) technology, which is the subject of U.S. Pat. No. 8,132,987.
Usually, smoldering combustion requires a short duration energy input, and the addition of an oxidant (e.g., oxygen or air) to initiate and sustain the smoldering combustion reaction. An example of a smoldering combustion reaction is that of a burning charcoal briquette. Smoldering combustion is normally only possible in the presence of a fuel source and a porous matrix. In the case of a charcoal briquette, the charcoal is both the fuel and the porous matrix; whereas for the STAR process, the fuel is an organic contaminant and the porous matrix is the subterranean volume of soil.
In the field of hydrogen production, there are many techniques available for the generation of hydrogen and these techniques are commonly grouped into methods that derive hydrogen from hydrocarbon fuels or from water. Of the methods that derive hydrogen from hydrocarbon fuels, steam reforming is the most common. Steam reforming involves the reaction of a hydrocarbon fuel with steam at high temperature (typically 700 to 1100 degrees Celsius) in the presence of a catalyst. Usually, in this process, steam reacts with methane in the presence of a nickel catalyst to yield carbon monoxide and hydrogen, and additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide in the presence of a copper or iron catalyst. The first reaction is strongly endothermic while the second reaction is mildly exothermic; thus, the first, high-temperature reaction requires the input of significant heat energy into the system for the process to proceed.
Smoldering combustion of organic fuels such as hydrocarbons is usually an exothermic reaction (net energy producing) that can be established with only a short duration, low-input of localized energy and then operates in a self-sustaining manner; in essence, the energy for the smoldering of the hydrocarbon fuels primarily comes from the inherent energy within the fuel themselves.
In addition, once smoldered, non-combustible materials within the organic fuels will remain as ash. The ash may include metals or phosphorus-containing compounds in concentrations of economic value. Recent studies have determined that biosolids—semi-solid organic materials from the treatment of sewage in waste water treatment plants—may contain metals and other materials such as phosphorus compounds that may be recovered if only they can be separated or removed from the organic material in which they reside.
One current method for separating inorganic materials of value from biosolids or other combustible materials is through the incineration of these materials and subsequent recovery of the inorganic materials from the ashes. Incineration, however, uses external fuel to drive the destruction of organic materials, thereby making the process more costly and less competitive from an economic perspective.